[ntp:questions] how did ntp service set the maxallowphaseoffset

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Tue Nov 19 02:45:44 UTC 2013


On 2013-11-18 01:30, xiaoniao112233 at gmail.com wrote:
> hello :
>     I had recently start a work about ntp service ,my friends and me use windows and linux to sync time in ntp.we could use w32time service to sync linux in ntp.In windows we could I found that in the registry:
> HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Config\ MaxAllowedPhaseOffset may be could set the offset time between the local time and the server that they will be synchronize. If out of range of MaxAllowedPhaseOffset in seconds ,they synchronize,otherwise not.
> But I have a question that Is there a paremeter in ntp service that control the offset like in registry above in windows.

W32tm is an SNTP service intended to synchronize time on
workstations in a domain to a domain controller at intervals.

NTP service is intended to maintain accurate time on clients
and servers across the internet, where the accuracy willdepend
on your budget and effort, from <100ms with poolservers to
<1us with reference clock hardware and kernel PPS support.

W32tm service parameters documented at
http://technet.microsoft.com/en-us/library/cc773263%28v=ws.10%29.aspx,
may be compared to options from NTP docs @ doc.ntp.org:

e.g.
Configuration Commands and Options
Miscellaneous Commands
tinker - modify sacred system parameters (dangerous)
http://doc.ntp.org/4.2.6p5/miscopt.html#tinker
for current stable release 4.2.6p5

tinker...

... panic panic
         Specifies the panic threshold in seconds with default 1000 s.
If set to zero, the panic sanity check is disabled and a clock offset
of any value will be accepted.

... step step
         Specifies the step threshold in seconds.
The default without this command is 0.128 s.
If set to zero, step adjustments will never occur.
Note: The kernel time discipline is disabled if the step threshold is
set to zero or greater than 0.5 s.

... stepout stepout
         Specifies the stepout threshold in seconds.
The default without this command is 900 s.
If set to zero, popcorn spikes will not be suppressed.


So tinker step is similar to W32tm MaxAllowedPhaseOffset except for
different service levels:
The default value for domain members is 300.
The default value for stand-alone clients and servers is 1.
and the W32tm slew requirement:
|CurrentTimeOffset| / (PhaseCorrectRate*UpdateInterval) < SystemClockRate / 2
-- 
-- 
Take care. Thanks, Brian Inglis


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